Analyte monitoring: stabilizer for subcutaneous glucose sensor with incorporated antiglycolytic agent

ABSTRACT

An analyte sensor including an antiglycolytic agent or a precursor thereof and a chelating agent that stabilizes the antiglycolytic agent positioned proximate to the working electrode of the sensor. Also provided are systems and methods of using the electrochemical analyte sensors in analyte monitoring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part, and claims the benefit ofpriority of U.S. patent application Ser. No. 11/322,165, filed Dec. 28,2005, now published as U.S. Patent Publication No. 2007/0149875, whichis incorporated herein by reference.

BACKGROUND

The monitoring of the level of glucose or other analytes, such aslactate or oxygen, in certain individuals is vitally important to theirhealth. High or low levels of glucose or other analytes may havedetrimental effects. For example, the monitoring of glucose isparticularly important to individuals with diabetes, as they mustdetermine when insulin is needed to reduce glucose levels in theirbodies or when additional glucose is needed to raise the level ofglucose in their bodies.

A conventional technique used by many diabetics for personallymonitoring their blood glucose level includes the periodic drawing ofblood, the application of that blood to a test strip, and thedetermination of the blood glucose level using calorimetric,electrochemical, or photometric detection. This technique does notpermit continuous or automatic monitoring of glucose levels in the body,but typically must be performed manually on a periodic basis.Unfortunately, the consistency with which the level of glucose ischecked varies widely among individuals. Many diabetics find theperiodic testing inconvenient and they sometimes forget to test theirglucose level or do not have time for a proper test. In addition, someindividuals wish to avoid the pain associated with the test. Thesesituations may result in hyperglycemic or hypoglycemic episodes. An invivo glucose sensor that continuously or automatically monitors theindividual's glucose level would enable individuals to more easilymonitor their glucose, or other analyte levels.

Analyte monitoring devices have been developed for continuous orautomatic monitoring of analytes, such as glucose, in the blood streamor interstitial fluid. Such devices include electrochemical sensors, atleast a portion of which are operably positioned in a blood vessel or inthe subcutaneous tissue of a patient.

Regardless of the type of analyte monitoring device employed, it hasbeen observed that transient, low readings may occur for a period oftime. These spurious low readings may occur during the first hours ofuse, or anytime thereafter. In certain embodiments, spurious lowreadings may occur during the night and sometimes are referred to as“night time dropouts”. For example, in the context of an operablypositioned continuous monitoring analyte sensor under the skin of auser, such spurious low readings may occur for a period of timefollowing sensor positioning and/or during the first nightpost-positioning. In many instances, the spurious low readings resolveafter a period of time. However, these transient, low readings imposeconstraints upon analyte monitoring during the period in which thespurious low readings are observed. Attempts to address this problemvary and include delaying reporting readings to the user until afterthis period of low readings passes after positioning of the sensor, orfrequent calibration of the sensor—both of which are inconvenient andneither of which is desirable.

As attention to analyte monitoring continues, there is an interest inanalyte monitoring protocols that do not exhibit, or at least minimize,spurious low readings, e.g., spurious readings following deviceplacement in a user and/or thereafter such as during the night. Spuriouslow readings may be caused by the presence of blood clots also known as“thrombi” that form as a result of insertion of the sensor in vivo. Suchclots exist in close proximity to a subcutaneous glucose sensor and havea tendency to “consume” glucose at a high rate, thereby lowering thelocal glucose concentration. Of particular interest are analytemonitoring compositions and protocols and that are capable ofsubstantially immediate and accurate analyte reporting to the user sothat spurious low readings, or frequent calibrations, are minimized orare non existent.

The present invention addresses these needs.

SUMMARY OF THE INVENTION

Embodiments of the invention include electrochemical analyte sensorshaving an antiglycolytic agent or a precursor thereof and a chelatingagent that stabilizes the antiglycolytic agent positioned proximate tothe working electrode of the sensor. Also provided are systems andmethods of using the electrochemical analyte sensors in analytemonitoring.

Other embodiments of the invention relate to methods and devices formonitoring of the level of an analyte using an in vivo or in vitroanalyte sensor, e.g., continuous and/or automatic in vivo or in vitromonitoring using an analyte sensor. Embodiments of the subject inventioninclude sensors that do not exhibit, or at least have a minimal periodof time in which, spurious, low reading are observed. The subjectinvention may be employed to minimize or eliminate spurious low analytereadings obtained at any time during sensor use, including a period oftime immediately after sensor activation (e.g., positioning of ananalyte sensor in or on a patient) and/or anytime thereafter.Embodiments include sensors in which at least a portion of the sensor isadapted to be positioned beneath the skin of a user and which areadapted for providing clinically accurate analyte data substantiallyimmediately after the sensor has been operably positioned in a patient(e.g., in the subcutaneous tissue, etc.) and/or without substantialinterruption due to spurious analyte readings.

Embodiments of the subject invention include calibrateable analytesensor devices in which the period of time when a first (or only)calibration is required, after positioning the sensor in a patient, issubstantially reduced (excluding factory-set calibration) and/or thenumber of calibrations is reduced, e.g., to three or less calibrations,e.g., two or less calibrations, e.g., one calibration or nocalibrations.

Embodiments of the subject devices include devices (e.g., analytesensors) that include an antiglycolytic agent or precursor thereof andone or more chelating agents. Such chelating agents may include borateminerals, boric acid or an equivalent compound.

Also provided are methods of determining the concentration of an analytein bodily fluid, where embodiments include determining the concentrationof an analyte in a bodily fluid without any, or with only a minimalperiod of time in which spurious, low readings are observed. Embodimentsinclude positioning an analyte sensor in a patient and determining, withclinical accuracy, the concentration of an analyte in bodily fluidsubstantially immediately following the operable positioning.

Embodiments of the subject methods include contacting an antiglycolyticagent or precursor thereof in combination with one or more chelatingagents to an analyte determination site, and determining theconcentration of an analyte at the site.

Embodiments of the subject methods include operably positioning a device(e.g., an analyte sensor) that includes an antiglycolytic agent orprecursor thereof and one or more chelating agents in a patient, anddetermining the concentration of an analyte using the sensor.

Embodiments of the subject methods include analyte determination methodshaving a substantially reduced period of time when a first (or only)calibration is required (excluding factory-set calibration), afterpositioning the sensor in a patient, and/or the number of calibrationsis reduced, e.g., to three or less calibrations, e.g., two or lesscalibrations, e.g., one calibration or no calibrations.

Also provided are methods of stabilizing an antiglycolytic agent withone or more chelating agents for use in an analyte biosensor.

Embodiments of the subject methods include coating an analyte sensorcontaining an antiglycolytic agent or precursor thereof with one or morechelating agents such as borate minerals, boric acid or an equivalentcompound. In other embodiments, an analyte determination site may becontacted with an antiglycolytic agent or precursor thereof and one ormore chelating agents such as borate minerals, boric acid, or anequivalent compound, prior to determining the concentration of ananalyte at the site.

Also provided are methods of manufacturing an electrochemical sensorcomprising an antiglycolytic agent or a precursor thereof and achelating agent positioned proximate to the working electrode of thesensor, including, but not limited to, formulation in the sensing layer,deposition over the surface of the sensing layer, formulation in themembrane, deposition over the membrane, deposition on the surface of thesensor, such as the working electrode, and the like.

Also provided are systems and kits.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings. It is emphasized that,according to common practice, the various features of the drawings arenot to-scale. On the contrary, the dimensions of the various featuresare arbitrarily expanded or reduced for clarity. Included in thedrawings are the following figures:

FIG. 1 shows a block diagram of an exemplary embodiment of an analytemonitor using an analyte sensor, according to the invention;

FIG. 2 is a top view of one embodiment of an analyte sensor, accordingto the invention;

FIG. 3A is a cross-sectional view of the analyte sensor of FIG. 2;

FIG. 3B is a cross-sectional view of another embodiment of an analytesensor, according to the invention;

FIG. 4A is a cross-sectional view of another embodiment of an analytesensor, according to the invention;

FIG. 4B is a cross-sectional view of a fourth embodiment of anotherembodiment of a sensor, according to the invention;

FIG. 5 is a cross-sectional view of another embodiment of an analytesensor, according to the invention;

FIG. 6 is an expanded top view of a tip-portion of the analyte sensor ofFIG. 6;

FIG. 7 is an expanded bottom view of a tip-portion of the analyte sensorof FIG. 6;

FIG. 8 is a side view of the analyte sensor of FIG. 2;

FIG. 9 is a cross-sectional view of an embodiment of an on-skin sensorcontrol unit, according to the invention;

FIG. 10 is a top view of a base of the on-skin sensor control unit ofFIG. 9;

FIG. 11 is a bottom view of a cover of the on-skin sensor control unitof FIG. 9;

FIG. 12 is a perspective view of the on-skin sensor control unit of FIG.9 on the skin of a patient;

FIG. 13A is a block diagram of one embodiment of an on-skin sensorcontrol unit, according to the invention;

FIG. 13B is a block diagram of another embodiment of an on-skin sensorcontrol unit, according to the invention;

FIG. 14 is a block diagram of one embodiment of a receiver/display unit,according to the invention;

FIG. 15A shows an experimental set-up that includes analyte sensors inbiofluid-containing tubes;

FIG. 15B shows a sensor in a plasma-containing tube;

FIG. 15C shows a sensor in a heparinized whole blood-containing tube;

FIG. 15D shows a sensor is a non heparinized whole blood containingtube;

FIG. 15E shows a graph of sensor readings according to the experimentalconditions;

FIG. 16 shows a graph of sensor readings of antiglycolytic sensors andcontrol sensors;

FIG. 17 shows a comparison of an antiglycolytic sensor and a controlsensor in vivo; and

FIG. 18 shows the effect of stress on glucose biosensors with andwithout the addition of boric acid. Boric acid and L-glyceraldehyde areincorporated into the outer membrane of the biosensors. The highbackground current is significantly reduced when boric acid is added tothe membrane formulation.

DEFINITIONS

Throughout embodiments of the application, unless a contrary intentionappears, the following terms refer to the indicated characteristics.

A “biological fluid” or “physiological fluid” or “bodily fluid”, is anybodily fluid in which an analyte can be measured, for example, blood,interstitial fluid, dermal fluid, sweat, tears, and urine. “Blood”includes whole blood and its cell-free components, including, plasma andserum.

A “counter electrode” refers to an electrode paired with the workingelectrode, through which passes a current equal in magnitude andopposite in sign to the current passing through the working electrode.In the context of the invention, the term “counter electrode” is meantto include counter electrodes which also function as referenceelectrodes (i.e., a counter/reference electrode).

An “electrochemical sensor” is a device configured to detect thepresence and/or measure the level of an analyte in a sample viaelectrochemical oxidation and reduction reactions on the sensor. Thesereactions are transduced to an electrical signal that can be correlatedto an amount, concentration, or level of an analyte in the sample.

“Electrolysis” is the electrooxidation or electroreduction of a compoundeither directly at an electrode or via one or more electron transferagents.

A compound is “immobilized” on a surface when it is entrapped on orchemically bound to the surface.

A “non-leachable” or “non-releasable” compound or a compound that is“non-leachably disposed” is meant to define a compound that is affixedon the sensor such that it does not substantially diffuse away from theworking surface of the working electrode for the period in which thesensor is used (e.g., the period in which the sensor is implanted in apatient or measuring a sample).

Components are “immobilized” within a sensor, for example, when thecomponents are covalently, ionically, or coordinatively bound toconstituents of the sensor and/or are entrapped in a polymeric orsol-gel matrix or membrane which precludes mobility. For example, incertain embodiments an antiglycolytic agent or precursor thereof may beimmobilized within a sensor.

An “electron transfer agent” is a compound that carries electronsbetween the analyte and the working electrode, either directly, or incooperation with other electron transfer agents. One example of anelectron transfer agent is a redox mediator.

A “working electrode” is an electrode at which the analyte (or a secondcompound whose level depends on the level of the analyte) iselectrooxidized or electroreduced with or without the agency of anelectron transfer agent.

A “working surface” is that portion of the working electrode which iscoated with or is accessible to the electron transfer agent andconfigured for exposure to an analyte-containing fluid.

A “sensing layer” is a component of the sensor which includesconstituents that facilitate the electrolysis of the analyte. Thesensing layer may include constituents such as an electron transferagent, a catalyst which catalyzes a reaction of the analyte to produce aresponse at the electrode, or both. In some embodiments of the sensor,the sensing layer is non-leachably disposed in proximity to or on theworking electrode.

A “non-corroding” conductive material includes non-metallic materials,such as carbon and conductive polymers.

When one item is indicated as being “remote” from another, this isreferenced that the two items are at least in different buildings, andmay be at least one mile, ten miles, or at least one hundred milesapart. When different items are indicated as being “local” to each otherthey are not remote from one another (for example, they can be in thesame building or the same room of a building). “Communicating”,“transmitting” and the like, of information reference conveying datarepresenting information as electrical or optical signals over asuitable communication channel (for example, a private or publicnetwork, wired, optical fiber, wireless radio or satellite, orotherwise). Any communication or transmission can be between deviceswhich are local or remote from one another. “Forwarding” an item refersto any means of getting that item from one location to the next, whetherby physically transporting that item or using other known methods (wherethat is possible) and includes, at least in the case of data, physicallytransporting a medium carrying the data or communicating the data over acommunication channel (including electrical, optical, or wireless).“Receiving” something means it is obtained by any possible means, suchas delivery of a physical item. When information is received it may beobtained as data as a result of a transmission (such as by electrical oroptical signals over any communication channel of a type mentionedherein), or it may be obtained as electrical or optical signals fromreading some other medium (such as a magnetic, optical, or solid statestorage device) carrying the information. However, when information isreceived from a communication it is received as a result of atransmission of that information from elsewhere (local or remote).

When two items are “associated” with one another they are provided insuch a way that it is apparent that one is related to the other such aswhere one references the other.

Items of data are “linked” to one another in a memory when a same datainput (for example, filename or directory name or search term) retrievesthose items (in a same file or not) or an input of one or more of thelinked items retrieves one or more of the others.

It will also be appreciated that throughout the present application,that words such as “cover”, “base” “front”, “back”, “top”, “upper”, and“lower” are used in a relative sense only.

“May” refers to optionally.

When two or more items (for example, elements or processes) arereferenced by an alternative “or”, this indicates that either could bepresent separately or any combination of them could be present togetherexcept where the presence of one necessarily excludes the other orothers.

Any recited method can be carried out in the order of events recited orin any other order which is logically possible. Reference to a singularitem, includes the possibility that there are plural of the same itempresent.

DETAILED DESCRIPTION

Before the present invention is described, it is to be understood thatthis invention is not limited to particular embodiments described, assuch may, of course, vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting, since the scope ofthe present invention will be limited only by the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges is also encompassed within the invention, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either or both ofthose included limits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present invention, the preferredmethods and materials are now described.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentinvention.

The figures shown herein are not necessarily drawn to scale, with somecomponents and features being exaggerated for clarity.

Electrochemical Analyte Sensors

Embodiments of the invention relate to electrochemical analyte sensorsincluding an antiglycolytic agent or a precursor thereof and a chelatingagent that stabilizes the antiglycolytic agent positioned proximate tothe working electrode of the sensor. It has been previously shown thatan antiglycolytic agent, such as L-glyceraldehyde, may be advantageouslyadded to a biosensor to reduce the local consumption of glucose bythrombi. While this advantageously prevents spurious glucose readings,glyceraldehydes have the disadvantage of degrading over time, therebycausing further interference with glucose readings. Biosensors must bestable at various temperatures over various lengths of time since theywill be subjected to a “shelf-life” prior to patient use. Embodiments ofthe invention demonstrate that use of a chelating agent such as borateminerals, boric acid or an equivalent compound, is capable of preventdegradation of the antiglycolytic agent, thereby stabilizing biosensorscontaining the antiglycolytic agents, such as L-glyceraldehyde.Accordingly,

As exemplified in Reaction Scheme 1, the antiglycolytic agentL-glyceraldehyde transforms to an unstable enol under stressedcondition, and decomposes rapidly to generate undescribable polymericmixtures.

As shown herein, the above reaction is prevented by adding a chelatingagent, e.g., borate, which stabilizes the antiglycolytic agent andprevents the rapid decomposition and rapid polymerization of theantiglycolytic agent. For example, a molecule of borate and twomolecules of L-glyceraldehyde will form a diglyceraldehyde boratecomplex, as shown below in Reaction Scheme 2, which is a stabilizedcomplex that does not decompose and rapidly polymerized as compared tothe absence of the chelating agent.

Embodiments of the invention include devices that include anantiglycolytic agent or precursor thereof and a chelating agent thatstabilizes the antiglycolytic agent or precursor thereof, e.g., analytesensors that include an antiglycolytic agent or precursor thereof and achelating agent. The antiglycolytic agent or precursor thereof and thechelating agent are collectively referred to herein as “active agent”.

The term “antiglycolytic” is used broadly herein to include anysubstance that at least retards glucose consumption of living cells. Theantiglycolytic agents or antiglycolytic agent precursors may be anysuitable antiglycolytic agents or precursors known or to be discovered.

Examples of antiglycolytic agents include, but are not limited to,fluorides, glyceraldehydes, mannose, glucosamine, mannoheptulose,sorbose-6-phophate, trehalose-6-phosphate, maleimide, iodoacetates, andthe like, and combinations thereof. Examples of antiglycolytic agentprecursors include, but are not limited to, enzymes, e.g.,trehalose-6-phosphate synthase, and the like. For example, theantiglycolytic agent may be glyceraldehydes, e.g., D-glyceraldehyde,L-glyceraldehyde, or a racemic mixture of D- and L-glyceraldehyde. Asnoted above, fluorides may be used, e.g., sodium fluoride, potassiumfluoride, etc.

Chelating agents, as used herein refer to compounds capable of formingtwo or more coordination bonds with organic compounds, therebystabilizing the organic compounds from degradation and decomposition.Examples of chelating agents suitable for use in the embodiments of theinvention include, but are not limited to, borate, boric acid, maingroup metals, such as Ca(II), and transition metals, such as, Cu (II),Zn(II), Co(II), V(IV), Mn(II), Ni(II), Fe(II), and the like. Additionalchelating agents that are capable of stabilizing the organic compoundsfrom degradation and decomposition include the Group IIIA metals, suchas Al, Ga, In, and Ti.

The amount of active agent included in a sensor may vary depending on avariety of factors such as the particular active agent used, theparticulars of the sensor, etc. In any event, an effective amount ofactive agent used—an amount sufficient to provide the requisitestabilized antiglycolytic result for the desired period of time. By wayof example, in embodiments using L-glyceraldehyde as an antiglycolyticagent, the amount of L-glyceraldehyde may range from about 1 microgramto about 2 milligrams, e.g., 10 micrograms to about 200 micrograms. Byway of example, in embodiments using boric acid as a chelating agent,the amount of boric acid may range from about 0.1 microgram to about 1milligrams, e.g., 1 micrograms to about 100 micrograms. As will beappreciated by one having skill in the art, each element of the activeagent may be present in equal quantities or in different quantities,depending on the specific antiglycolytic agent and chelating agentselected for use.

Embodiments of the invention are applicable to an analyte monitoringsystem using a sensor at least a portion of which is positioned beneaththe skin of the user for the in vivo determination of a concentration ofan analyte, including glucose, lactate, and the like, in a bodily fluid.The sensor may be, for example, subcutaneously positioned in a patientfor the continuous or periodic monitoring an analyte in a patient'sinterstitial fluid. This may be used to infer the glucose level in thepatient's bloodstream. The sensors of the subject invention also includein vivo analyte sensors for insertion into a vein, artery, or otherportion of the body containing fluid. A sensor of the subject inventionmay be configured for monitoring the level of the analyte over a timeperiod which may range from hours, days, weeks, or longer, as describedin greater detail below.

Embodiments of the invention also apply to an in vitro analytemonitoring system. For example, a system in which bodily fluid isobtained and contacted with an analyte sensor above the skin. Suchsystems include, but are not limited to, skin opening (e.g., a laser,lancet, or the like) and sampling devices adapted to determine theconcentration of an analyte in a sample of bodily fluid obtained fromthe skin opening, e.g., by periodically or continuously sampling fluidexuded at the site. The skin opening device and sampling device may beintegrated in a single unit or otherwise. Embodiments of the inventionare described primarily with respect to an analyte sensor in which atleast a portion of which is operably positioned under the skin of thepatient, where such description is for exemplary purposes only and is inno way intended to limit the scope of the invention in any way. It is tobe understood that the subject invention may be applicable to differentanalyte sensors, e.g., above-skin analyte sensors.

The subject invention includes devices and methods of analyteconcentration determined that have at least a substantially reduced(including completely eliminated) period of spurious, low analytereadings. In this manner, reportable analyte results may be obtainedwith a minimal, if any, time delay and/or interruption due to spuriouslow analyte readings.

Embodiments include positioning devices and systems, and methods thatprovide clinically accurate analyte data (e.g., relative to a reference)substantially immediately, as shown by any suitable technique known tothose of skill in the art, e.g., a Clark Error Grid, Parks Error Grid,Continuous Glucose Error Grid, MARD analysis, and the like. For example,in those embodiments in which the sensor is a continuous sensor and atleast a portion of the sensor is adapted to be positioned under the skinof a patient, the sensor is adapted to provide clinically accurateanalyte data (e.g., relative to a reference) substantially immediatelyafter the sensor is operably positioned in a patient. In other words,the waiting period from the time a sensor is positioned in a user andthe time clinically accurate data may be obtained and used by the user,is greatly reduced relative to prior art devices that require a greaterwaiting period before accurate analyte data may be obtained and used bya user. By “substantially immediately” is meant from about 0 hours toless than about 5 hours, e.g., from about 0 hours to about 3 hours,e.g., from about 0 hours to less than about 1 hour, e.g., from about 30minutes or less, where in many embodiments the sensors according to thesubject invention are capable of providing clinically accurate analytedata once the sensor has been operatively positioned in the patient.

The active-agent containing devices may be analyte sensors in certainembodiments, or may be a structure that is positionable near an analytedetermination site (a bodily fluid sampling site), e.g., near an analytesensor such as near a wholly or partially implantable sensor. In certainembodiments, the structure may be a sensor insertion device, drugdelivery device (e.g., insulin delivery device), etc. In certainembodiments, the active agent-containing device may be an active agentdelivery device. In further describing the subject invention, theinvention is described primarily with respect to anactive-agent-containing analyte sensor, where such description is forexemplary purposes only and is in no way intended to limit the scope ofthe invention in any way. It is to be understood that an active agentmay be associated with devices other than analyte sensors or otherwisecontacted with an appropriate area of a patient.

In certain embodiments, the active agent may not be carried by a device,i.e. independent of the device, but rather may be otherwise applied ator substantially near the analyte determination site on the skin of asubject, such as the forearm, abdomen, and the like. Accordingly,embodiments include systems having an active agent delivery unit and ananalyte sensor. In such embodiments, the active agent is formulated fortransdermal delivery by a topical route, such as topical application tothe skin of a subject.

The active agent employed in the subject invention may be deliveredtransdermally, by a topical route, formulated as applicator sticks,solutions, suspensions, emulsions, gels, creams, ointments, pastes,jellies, paints, powders, and aerosols. For example, embodiments mayinclude an active agent in the form of a discrete patch or film orplaster or the like adapted to remain in intimate contact with theepidermis of the recipient for a period of time. For example, suchtransdermal patches may include a base or matrix layer, e.g., polymericlayer, in which active agent is retained. The base or matrix layer maybe operably associated with a support or backing. Active agents suitablefor transdermal administration may also be delivered by iontophoresisand may take the form of an optionally buffered aqueous solution thatincludes the active agent. Suitable formulations may include citrate orbis/tris buffer (pH 6) or ethanol/water and contain a suitable amount ofactive ingredient. Active agents of the subject invention may be adaptedfor parenteral administration, including intravenous (“IV”)administration, intramuscular (“IM”), subcutaneous (“SC” or “SQ”),mucosal. The formulations for such administration may include a solutionof the active agent dissolved in a pharmaceutically acceptable carrier.Among the acceptable vehicles and solvents that may be employed,include, but are not limited to, water and Ringer's solution, anisotonic sodium chloride, etc. Active agent may be formulated intopreparations for injection by dissolving, suspending or emulsifying themin an aqueous or nonaqueous solvent, such as vegetable or other similaroils, synthetic aliphatic acid glycerides, esters of higher aliphaticacids or propylene glycol; and if desired, with conventional additivessuch as solubilizers, isotonic agents, suspending agents, emulsifyingagents, stabilizers and preservatives. These solutions are sterile andgenerally free of undesirable matter.

In other embodiments, the active agent may be delivered by the use ofliposomes which fuse with the cellular membrane or are endocytosed,i.e., by employing ligands attached to the liposome, or attacheddirectly to the oligonucleotide, that bind to surface membrane proteinreceptors of the cell resulting in endocytosis. By using liposomes,particularly where the liposome surface carries ligands specific fortarget cells, or are otherwise preferentially directed to a specificorgan, one can focus the delivery of the pharmacological agent into thetarget cells in vivo. (See, e.g., Al-Muhammed, J. Microencapsul.13:293-306, 1996; Chonn, Curr. Opin. Biotechnol. 6:698-708, 1995; Ostro,Am. J. Hosp. Pharm. 46:1576-1587, 1989). Methods for preparing liposomalsuspensions are known in the art and thus will not be described hereinin great detail.

Embodiments may also include administration of active agent using anactive agent delivery device such as, but not limited to, pumps(implantable or external devices and combinations of both (e.g., certaincomponents may be implantable and others may be external to the bodysuch as controls for the implantable components), epidural injectors,syringes or other injection apparatus, catheter and/or reservoiroperably associated with a catheter, etc. For example, in certainembodiments a delivery device employed to deliver active agent to asubject may be a pump, syringe, catheter or reservoir operablyassociated with a connecting device such as a catheter, tubing, or thelike. Containers suitable for delivery of active agent to an activeagent administration device include instruments of containment that maybe used to deliver, place, attach, and/or insert the active agent intothe delivery device for administration of the active agent to a subjectand include, but are not limited to, vials, ampules, tubes, capsules,bottles, syringes and bags. Embodiments may also include administrationof an active agent via a biodegradable implant active agent deliverydevice. Such may be accomplished by employing syringes to deposit such abiodegradable delivery device under the skin of a subject. The implantsdegrade completely, so that removal is not necessary.

Embodiments may include employing an electrode to deliver the activeagent to a subject. For example, an electrode may be used that has asmall port at its tip which is connected to a reservoir or pumpcontaining an active agent. The active agent delivery electrode may beimplanted using any suitable technique such as surgical cut down,laproscopy, endoscopy, percutaneous procedure, and the like. In certainembodiments a reservoir or pump may also be implanted in the subject'sbody. The active agent delivery electrode, or other analogous device,may be controllable such that the amount of active agent delivered, therate at which the active agent may be delivered, and the time periodover which the active agent may be delivered, etc., may be controllableand may be adjusted, e.g., by a user and/or healthcare worker.

Accordingly, embodiments include contacting an analyte determinationsite with an active agent or agents, and determining the concentrationof an analyte, where the contacting may be by way of an analyte sensoror other structure, transdermal administration, parenteraladministration, etc.

As described above, analyte sensors may include active agents. Thesensors may include or incorporate active agents thereof in any suitablemanner. At least a portion of the sensor (and/or other structure), e.g.,a bodily fluid-contacting portion, includes active agents, and incertain embodiments substantially the entire sensor may include theactive agent. Active agents may be immobilized on a surface of thesensor or may be configured to diffuse away from the sensor surface.

In certain embodiments, the active agent is a coating on at least aportion of the sensor, such as proximate to or directly on the workingelectrode and/or reference/counter electrode, on the sensing layer, onthe flux-limiting membrane. In certain embodiments, the active agent isincorporated, e.g., embedded, or otherwise integrated into the sensor,such as the sensing layer formulation, the redox polymer formulation,the flux-limiting membrane formulation.

As will be described in greater detail below, an analyte sensor mayinclude a matrix component such as a membrane. The membrane may be, forexample, a mass transfer limiting membrane. In certain embodiments, themembrane may include the active agent such that the membrane may includea coating thereof such that the active agent may be incorporated as athin coating positioned about a surface of the membrane, e.g., a fluidcontacting surface. The amount of active agent to be included may bereadily controlled by applying multiple thin coats thereof, e.g., andallowing it to dry between coats.

The thickness of a coating will be minimal so as not to appreciablyincrease the thickness of the membrane. In many embodiments, thethickness is substantially uniform. The thickness in certain embodimentsmay range from about 0.1 microns to about 100 microns, e.g., from about1 micron to about 10 microns.

Alternatively or in addition to a coating, an active agent may beincorporated within the material of the sensor, e.g., incorporatedwithin the material of a sensor membrane itself, the sensing layer ofthe working electrode, the redox polymer, the flux-limiting membrane,and the like. For example, membranes are often applied to a sensor via aspraying or dipping process, wherein the membrane material is dissolvedin a solvent and the resulting solution is applied to the sensorsubstrate. In this case the active agent may simply be co-dissolved withthe membrane material in the solvent. This results in a sensor withactive agent dispersed evenly throughout the sensor membrane.

The sensors may also have the ability to emit or diffuse an active agentat a controllable rate, e.g., may include a controlled release, such asa time release, formulation. For example, a sensor (e.g., a membrane ofthe sensor) may include a formulation that is designed to release anactive agent gradually over time, e.g., over about a period of timecommensurate with a period of time in which a sensor exhibits spuriouslow glucose readings post-sensor insertion, e.g., about 1 hour to about24 hours in certain embodiments. A controlled release formulation mayemploy a polymer or other non-antiglycolytic agent material to controlthe release of the active agent. The active agent release rate may beslowed by diffusion through the polymer, or the antiglycolytic agent orprecursor may be released as the polymer degrades or disintegrates inthe body.

The active agent may be added to the sensor during fabrication of thesensor and/or may be applied to the sensor after it has been fabricated.For example, a coating containing an active agent or agents thereof maybe applied to the sensor after it has been fabricated.

Active agents may be applied to the sensor by any of a variety ofmethods, e.g., by spraying the active agent onto the sensor or bydipping the sensor into the active agent, by coating the active agentwith a slotted die, or otherwise immersing or flooding the sensor withthe active agent. In addition, the active agent may be incorporated intothe sensing layer formulation, or redox polymer formulation, theflux-limiting membrane formation.

The active agent thereof may be used with any analyte sensor, e.g., ananalyte sensor configured so that at least a portion of the sensor isoperably positionable under the skin of a patient for the concentrationdetermination of an analyte. Of interest are analyte sensors that arecapable of providing analyte data automatically (continuously orperiodically) for about one hour or more, e.g., about a few hours ormore, e.g., about a few days of more, e.g., about three or more days,e.g., about five days or more, e.g., about seven days or more, e.g.,about several weeks or months.

Representative active-agent containing analyte sensors and analytemonitoring systems that include active agent containing-analyte sensorsaccording to the subject invention are now described, where suchdescription is for exemplary purposes only and is in no way intended tolimit the scope of the invention.

Antiglycolytic Analyte Sensors and Sensor Systems

The analyte sensors and analyte monitoring systems of the embodiments ofthe invention may be utilized under a variety of conditions. Theparticular configuration of an antiglycolytic and chelating agentstabilizer sensor and other units used in an analyte monitoring systemmay depend on the use for which the sensor and system are intended andthe conditions under which the sensor and system will operate. As notedabove, embodiments include a sensor configured for implantation into apatient or user. The term “implantation” is meant broadly to includewholly implantable sensors and sensors in which only a portion of whichis implantable under the skin and a portion of which resides above theskin, e.g., for contact to a transmitter, receiver, transceiver,processor, etc. For example, implantation of the sensor may be made inthe arterial or venous systems for direct testing of analyte levels inblood. Alternatively, a sensor may be implanted in the interstitialtissue for determining the analyte level in interstitial fluid. Thislevel may be correlated and/or converted to analyte levels in blood orother fluids. The site and depth of implantation may affect theparticular shape, components, and configuration of the sensor.Subcutaneous implantation may be desired, in some cases, to limit thedepth of implantation of the sensor. Sensors may also be implanted inother regions of the body to determine analyte levels in other fluids.Examples of suitable sensors for use in the analyte monitoring systemsof the invention are described in U.S. Pat. Nos. 6,134,461 and6,175,752.

An exemplary embodiment of an analyte monitoring system 40 for use withan implantable antiglycolytic sensor 42, e.g., for use with asubcutaneously implantable antiglycolytic sensor, is illustrated inblock diagram form in FIG. 1. Said analyte monitoring system mayoptionally include borate minerals or boric acid or any precursorthereof. The analyte monitoring system 40 includes, at minimum, a sensor42 that includes an antiglycolytic agent or precursor thereof, a portionof the sensor which is configured for implantation (e.g., subcutaneous,venous, or arterial implantation) into a patient, and a sensor controlunit 44. The antiglycolytic sensor 42 is coupleable to the sensorcontrol unit 44 which may be attachable to the skin of a patient. Thesensor control unit 44 operates the sensor 42, including, for example,providing a voltage across the electrodes of the sensor 42 andcollecting signals from the sensor 42.

The sensor control unit 44 may evaluate the signals from the sensor 42and/or transmit the signals to one or more optional receiver/displayunits 46, 48 for evaluation. The sensor control unit 44 and/or thereceiver/display units 46, 48 may display or otherwise communicate thecurrent level of the analyte. Furthermore, the sensor control unit 44and/or the receiver/display units 46, 48 may indicate to the patient,via, for example, an audible, visual, or other sensory-stimulatingalarm, when the level of the analyte is at or near a threshold level. Insome embodiments, an electrical shock may be delivered to the patient asa warning through one of the electrodes or the optional temperatureprobe of the sensor. For example, if glucose is monitored then an alarmmay be used to alert the patient to a hypoglycemic or hyperglycemicglucose level and/or to impending hypoglycemia or hyperglycemia.

Antiglycolytic/Antiglycolytic Precursor-Containing Sensors

The sensor 42 includes an antiglycolytic agent or precursor thereof anda chelating agent, including boric acid or borate minerals, as describedherein, and includes at least one working electrode 58 and a substrate50, as shown for example in FIG. 2. The sensor 42 may also include atleast one counter electrode 60 (or counter/reference electrode) and/orat least one reference electrode 62 (see for example FIG. 7). Thecounter electrode 60 and/or reference electrode 62 may be formed on thesubstrate 50 or may be separate units. For example, the counterelectrode and/or reference electrode may be formed on a second substratewhich is also implantable in the patient or, for some embodiments of thesensors the counter electrode and/or reference electrode may be placedon the skin of the patient with the working electrode or electrodesbeing implanted into the patient. The use of an on-the-skin counterand/or reference electrode with an implantable working electrode isdescribed in, e.g., U.S. Pat. No. 5,593,852.

The working electrode or electrodes 58 are formed using conductivematerials 52. The counter electrode 60 and/or reference electrode 62, aswell as other optional portions of the sensor 42, such as a temperatureprobe 66 (see for example FIG. 7), may also be formed using conductivematerial 52. The conductive material 52 may be formed over a smoothsurface of the substrate 50 or within channels 54 formed by, forexample, embossing, indenting or otherwise creating a depression in thesubstrate 50.

A sensing layer 64 (see for example FIGS. 3 and 4 and 5) may be providedproximate to or on at least one of the working electrodes 58 tofacilitate the electrochemical detection of the analyte and thedetermination of its level in the sample fluid, particularly if theanalyte can not be electrolyzed at a desired rate and/or with a desiredspecificity on a bare electrode. The sensing layer 64 may include anelectron transfer agent to transfer electrons directly or indirectlybetween the analyte and the working electrode 58. The sensing layer 64may also contain a catalyst to catalyze a reaction of the analyte. Thecomponents of the sensing layer may be in a fluid or gel that isproximate to or in contact with the working electrode 58. Alternatively,the components of the sensing layer 64 may be disposed in a polymeric orsol-gel matrix that is proximate to or on the working electrode 58. Incertain embodiments, the components of the sensing layer 64 arenon-leachably disposed within the sensor 42 and in certain embodimentsthe components of the sensor 42 are immobilized within the sensor 42.

In addition to the electrodes 58, 60, 62 and the sensing layer 64, thesensor 42 may also include optional components such as one or more ofthe following: a temperature probe 66 (see for example FIGS. 5 and 7), amass transport limiting layer 74, e.g., a matrix such as a membrane orthe like, (see for example FIG. 8), a biocompatible layer 75 (see forexample FIG. 8), and/or other optional components, as described below.Each of these items enhances the functioning of and/or results from thesensor 42, as discussed below.

The substrate 50 may be formed using a variety of non-conductingmaterials, including, for example, polymeric or plastic materials andceramic materials. Suitable materials for a particular sensor 42 may bedetermined, at least in part, based on the desired use of the sensor 42and properties of the materials.

In addition to considerations regarding flexibility, it is oftendesirable that a sensor 42 should have a substrate 50 which isnon-toxic. Preferably, the substrate 50 is approved by one or moreappropriate governmental agencies or private groups for in vivo use.Although the substrate 50 in at least some embodiments has uniformdimensions along the entire length of the sensor 42, in otherembodiments, the substrate 50 has a distal end 67 and a proximal end 65with different widths 53, 55, respectively, as illustrated in FIG. 2.

At least one conductive trace 52 may be formed on the substrate for usein constructing a working electrode 58. In addition, other conductivetraces 52 may be formed on the substrate 50 for use as electrodes (e.g.,additional working electrodes, as well as counter, counter/reference,and/or reference electrodes) and other components, such as a temperatureprobe. The conductive traces 52 may extend most of the distance along alength 57 of the sensor 50, as illustrated in FIG. 2, although this isnot necessary. The conductive traces may be formed using a conductivematerial 56 such as carbon (e.g., graphite), a conductive polymer, ametal or alloy (e.g., gold or gold alloy), or a metallic compound (e.g.,ruthenium dioxide or titanium dioxide), and the like. Conductive traces52 (and channels 54, if used) may be formed with relatively narrowwidths. In embodiments with two or more conductive traces 52 on the sameside of the substrate 50, the conductive traces 52 are separated bydistances sufficient to prevent conduction between the conductive traces52. The working electrode 58 and the counter electrode 60 (if a separatereference electrode is used) may be made using a conductive material 56,including carbon.

The reference electrode 62 and/or counter/reference electrode may beformed using conductive material 56 that is a suitable referencematerial, for example silver/silver chloride or a non-leachable redoxcouple bound to a conductive material, for example, a carbon-bound redoxcouple. The electrical contact 49 may be made using the same material asthe conductive material 56 of the conductive traces 52, oralternatively, may be made from a carbon or other non-metallic material,including a conducting polymer.

A number of exemplary electrode configurations are described below,however, it will be understood that other configurations may also beused. In certain embodiments, e.g., illustrated in FIG. 3A, the sensor42 includes two working electrodes 58 a, 58 b and one counter electrode60, which also functions as a reference electrode. In anotherembodiment, the sensor includes one working electrode 58 a, one counterelectrode 60, and one reference electrode 62, as shown for example inFIG. 3B. Each of these embodiments is illustrated with all of theelectrodes formed on the same side of the substrate 50. Alternatively,one or more of the electrodes may be formed on an opposing side of thesubstrate 50. In another embodiment, two working electrodes 58 and onecounter electrode 60 are formed on one side of the substrate 50 and onereference electrode 62 and a temperature probe 66 are formed on anopposing side of the substrate 50, for example as illustrated in FIG. 6.The opposing sides of the tip of this embodiment of the sensor 42 areillustrated in FIGS. 6 and 7.

Some analytes, such as oxygen, may be directly electrooxidized orelectroreduced on the working electrode 58. Other analytes, such asglucose and lactate, require the presence of at least one electrontransfer agent and/or at least one catalyst to facilitate theelectrooxidation or electroreduction of the analyte. Catalysts may alsobe used for those analyte, such as oxygen, that can be directlyelectrooxidized or electroreduced on the working electrode 58. For theseanalytes, each working electrode 58 has a sensing layer 64 formedproximate to or on a working surface of the working electrode 58. Inmany embodiments, the sensing layer 64 is formed near or on only a smallportion of the working electrode 58, e.g., near a tip of the sensor 42.

The sensing layer 64 includes one or more components designed tofacilitate the electrolysis of the analyte. The sensing layer 64 may beformed as a solid composition of the desired components (e.g., anelectron transfer agent and/or a catalyst). These components may benon-leachable from the sensor 42 and may be immobilized on the sensor42. Examples of immobilized sensing layers are described in, e.g., U.S.Pat. Nos. 5,262,035; 5,264,104; 5,264,105; 5,320,725; 5,593,852; and5,665,222; and PCT Patent Application No. US98/02403 entitled “SoybeanPeroxidase Electrochemical Sensor”.

Sensors having multiple working electrodes 58 a may also be used, e.g.,and the signals therefrom may be averaged or measurements generated atthese working electrodes 58 a may be averaged. In addition, multiplereadings at a single working electrode 58 a or at multiple workingelectrodes may be averaged.

In many embodiments, the sensing layer 64 contains one or more electrontransfer agents in contact with the conductive material 56 of theworking electrode 58, as shown in FIGS. 3A and 3B. Useful electrontransfer agents and methods for producing them are described in, e.g.,U.S. Pat. Nos. 5,264,104; 5,356,786; 5,262,035; 5,320,725, 6,175,752,and 6,329,161.

The sensing layer 64 may also include a catalyst which is capable ofcatalyzing a reaction of the analyte. The catalyst may also, in someembodiments, act as an electron transfer agent.

To electrolyze the analyte, a potential (versus a reference potential)is applied across the working and counter electrodes 58, 60. When apotential is applied between the working electrode 58 and the counterelectrode 60, an electrical current will flow. Those skilled in the artwill recognize that there are many different reactions that will achievethe same result; namely the electrolysis of an analyte or a compoundwhose level depends on the level of the analyte.

A variety of optional items may be included in the sensor. One optionalitem is a temperature probe 66 (see for example FIGS. 5 and 7). Oneexemplary temperature probe 66 is formed using two probe leads 68, 70connected to each other through a temperature-dependent element 72 thatis formed using a material with a temperature-dependent characteristic.An example of a suitable temperature-dependent characteristic is theresistance of the temperature-dependent element 72.

The temperature probe 66 may provide a temperature adjustment for theoutput from the working electrode 58 to offset the temperaturedependence of the working electrode 58.

The sensors of the subject invention are biocompatible. Biocompatibilitymay be achieved in a number of different manners. For example, anoptional biocompatible layer 74 may be formed over at least that portionof the sensor 42 which is inserted into the patient, for example asshown in FIG. 8.

An interferant-eliminating layer (not shown) may be included in thesensor 42. The interferant-eliminating layer may include ioniccomponents, such as, for example, NAFION or the like, incorporated intoa polymeric matrix to reduce the permeability of theinterferant-eliminating layer to ionic interferants having the samecharge as the ionic components.

A mass transport limiting layer 74 may be included with the sensor toact as a diffusion-limiting barrier to reduce the rate of mass transportof the analyte, for example, glucose or lactate, into the region aroundthe working electrodes 58.

Exemplary layers that may be used are described for example, in U.S.Pat. No. 6,881,551.

A sensor of the subject invention may be adapted to be a replaceablecomponent in an in vivo analyte monitor, and particularly in animplantable analyte monitor. In many embodiments, the sensor is capableof operation over a period of days or more, e.g., a period of operationmay be at least about one day, e.g., at least about three days, e.g., atleast about one week or more. The sensor may then be removed andreplaced with a new sensor.

Any suitable device may be used to insert a sensor of the subjectinvention into the patient (e.g., in the subcutaneous tissue or thelike). Exemplary insertion devices that may be used are described forexample, in U.S. Pat. No. 6,175,752.

In operation, a sensor is placed within or next to an insertion deviceand then a force is provided against the insertion device and/or sensorto carry the sensor 42 into the skin of the patient. The insertiondevice is optionally pulled out of the skin with the sensor remainingbeneath the skin, e.g., in the subcutaneous tissue, due to frictionalforces between the sensor and the patient's tissue.

In certain embodiments, the sensor is injected between about 2 to about12 mm into the interstitial tissue of the patient for subcutaneousimplantation. Other embodiments of the invention may include sensorsimplanted in other portions of the patient, including, for example, inan artery, vein, or organ. The depth of implantation varies depending onthe desired implantation target.

Although a sensor of the subject invention may be inserted anywhere inthe body, it is often desirable that the insertion site be positioned sothat an on-skin sensor control unit 44 may be concealed. In addition, itis often desirable that the insertion site be at a place on the bodywith a low density of nerve endings to reduce the pain to the patient.Examples of sites for insertion of the sensor 42 and positioning of theon-skin sensor control unit 44 include but are not limited to theabdomen, thigh, leg, upper arm, and shoulder.

The on-skin sensor control unit 44 is configured to be placed on theskin of a patient. One embodiment of the on-skin sensor control unit 44has a thin, oval shape to enhance concealment, as illustrated in FIGS.9-11. However, other shapes and sizes may be used. The on-skin sensorcontrol unit 44 includes a housing 45, as illustrated in FIGS. 9-11. Theon-skin sensor control unit 44 is typically attachable to the skin 75 ofthe patient, as illustrated in FIG. 12. Another method of attaching thehousing 45 of the on-skin sensor control unit 44 to the skin 75 includesusing a mounting unit 77 which includes an opening 79 through which thesensor 42 maybe inserted. Additional detailed description of the on-skinsensor control unit and 44 and the associated electronic components areprovided for example, in U.S. Pat. No. 6,175,752.

The sensor 42 and the electronic components within the on-skin sensorcontrol unit 44 are coupled via conductive contacts 80. The one or moreworking electrodes 58, counter electrode 60 (or counter/referenceelectrode), optional reference electrode 62, and optional temperatureprobe 66 are attached to individual conductive contacts 80. In theillustrated embodiment of FIGS. 9-11, the conductive contacts 80 areprovided on the interior of the on-skin sensor control unit 44.

The on-skin sensor control unit 44 may include at least a portion of theelectronic components that operate the sensor 42 and the analytemonitoring device system 40. One embodiment of the electronics in theon-skin control unit 44 is illustrated as a block diagram in FIG. 13A.The electronic components of the on-skin sensor control unit 44 mayinclude a power supply 95 for operating the on-skin control unit 44 andthe sensor 42, a sensor circuit 97 for obtaining signals from andoperating the sensor 42, a measurement circuit 96 that converts sensorsignals to a desired format, and a processing circuit 109 that, atminimum, obtains signals from the sensor circuit 97 and/or measurementcircuit 96 and provides the signals to an optional transmitter 98. Insome embodiments, the processing circuit 109 may also partially orcompletely evaluate the signals from the sensor 42 and convey theresulting data to the optional transmitter 98 and/or activate anoptional alarm system 94 (see for example FIG. 13B) if the analyte levelexceeds a threshold. The processing circuit 109 often includes digitallogic circuitry.

The on-skin sensor control unit 44 may optionally contain a transmitteror transceiver 98 for transmitting the sensor signals or processed datafrom the processing circuit 109 to a receiver (or transceiver)/displayunit 46, 48; a data storage unit 102 for temporarily or permanentlystoring data from the processing circuit 109; a temperature probecircuit 99 for receiving signals from and operating a temperature probe66; a reference voltage generator 101 for providing a reference voltagefor comparison with sensor-generated signals; and/or a watchdog circuit103 that monitors the operation of the electronic components in theon-skin sensor control unit 44. Moreover, the sensor control unit 44 mayinclude a bias control generator 105 to correctly bias analog anddigital semiconductor devices, an oscillator 107 to provide a clocksignal, and a digital logic and timing component 109 to provide timingsignals and logic operations for the digital components of the circuit.

FIG. 13B illustrates a block diagram of another exemplary on-skincontrol unit 44 that also includes optional components such as areceiver (or transceiver) 99 to receive, for example, calibration data;a calibration storage unit 100 to hold, for example, factory-setcalibration data, calibration data obtained via the receiver 99 and/oroperational signals received, for example, from a receiver/display unit46, 48 or other external device; an alarm system 104 for warning thepatient; and a deactivation switch 111 to turn off the alarm system.

Functions of the analyte monitoring system 40 and the sensor controlunit 44 may be implemented using either software routines, hardwarecomponents, or combinations thereof. The hardware components may beimplemented using a variety of technologies, including, for example,integrated circuits or discrete electronic components. The use ofintegrated circuits typically reduces the size of the electronics, whichin turn may result in a smaller on-skin sensor control unit 44.

The electronics in the on-skin sensor control unit 44 and the sensor 42are operated using a power supply 95. The sensor control unit 44 mayalso optionally include a temperature probe circuit 99.

The output from the sensor circuit 97 and optional temperature probecircuit is coupled into a measurement circuit 96 that obtains signalsfrom the sensor circuit 97 and optional temperature probe circuit 99and, at least in some embodiments, provides output data in a form that,for example can be read by digital circuits.

In some embodiments, the data from the processing circuit 109 isanalyzed and directed to an alarm system 94 (see for example FIG. 13B)to warn the user.

In some embodiments, the data (e.g., a current signal, a convertedvoltage or frequency signal, or fully or partially analyzed data) fromprocessing circuit 109 is transmitted to one or more receiver/displayunits 46, 48 using a transmitter 98 in the on-skin sensor control unit44. The transmitter has an antenna 93 formed in the housing 45.

In addition to a transmitter 98, an optional receiver 99 may be includedin the on-skin sensor control unit 44 or elsewhere. In some cases, thetransmitter 98 is a transceiver, operating as both a transmitter and areceiver. The receiver 99 (and/or receiver display/units 46, 48) may beused to receive calibration data for the sensor 42. The calibration datamay be used by the processing circuit 109 to correct signals from thesensor 42. This calibration data may be transmitted by thereceiver/display unit 46, 48 or from some other source such as a controlunit in a doctor's office.

Calibration data may be obtained in a variety of ways. For instance, thecalibration data may simply be factory-determined calibrationmeasurements which may be input into the on-skin sensor control unit 44using the receiver 99 or may alternatively be stored in a calibrationdata storage unit 100 within the on-skin sensor control unit 44 itselfor elsewhere such as, e.g., receiver display/units 46, 48, (in whichcase a receiver 99 may not be needed). The calibration data storage unit100 may be, for example, a readable or readable/writeable memorycircuit.

Alternative or additional calibration data may be provided based ontests performed by a doctor or some other professional or by the patienthimself. For example, it is common for diabetic individuals to determinetheir own blood glucose concentration using commercially availabletesting kits. The result of this test is input into the on-skin sensorcontrol unit 44 (and/or receiver display/units 46, 48) either directly,if an appropriate input device (e.g., a keypad, an optical signalreceiver, or a port for connection to a keypad or computer) isincorporated in the on-skin sensor control unit 44, or indirectly byinputting the calibration data into the receiver/display unit 46, 48 andtransmitting the calibration data to the on-skin sensor control unit 44.

Other methods of independently determining analyte levels may also beused to obtain calibration data. This type of calibration data maysupplant or supplement factory-determined calibration values.

In some embodiments of the invention, calibration data may be requiredat periodic intervals, for example, about every ten hours, or abouteight hours, about once a day, or about once a week, to confirm thataccurate analyte levels are being reported. Calibration may also berequired each time a new sensor 42 is implanted or if the sensor exceedsa threshold minimum or maximum value or if the rate of change in thesensor signal exceeds a threshold value. In some cases, it may benecessary to wait a period of time after the implantation of the sensor42 before calibrating to allow the sensor 42 to achieve equilibrium. Insome embodiments, the sensor 42 is calibrated only after it has beeninserted. In other embodiments, no calibration of the sensor 42 isneeded (e.g., a factory calibration may be sufficient).

Regardless of the type of analyte monitoring system employed, it hasbeen observed that transient, low readings may occur for a period oftime. These anomalous low readings may occur during the first hours ofuse, or anytime thereafter. In certain embodiments, spurious lowreadings may occur during the night and may be referred to as “nighttime dropouts”. For example, in the context of an operably positionedcontinuous monitoring analyte sensor under the skin of a user, suchspurious low readings may occur for a period of time following sensorpositioning and/or during the first night post-positioning. In manyinstances, the low readings resolve after a period of time. However,these transient, low readings put constraints analyte monitoring duringthe low reading period. Attempts to address this problem vary andinclude delaying calibration and/or reporting readings to the user untilafter this period of low readings passes after positioning of the sensoror frequent calibration of the sensor-both of which are inconvenient andneither of which is desirable.

However, as noted above embodiments of the subject invention have atleast a minimal period, if at all, of spurious low readings, i.e., asubstantially reduced sensor equilibration period, includingsubstantially no equilibration period. In this regard, in thoseembodiments in which an initial post-positioning calibration isrequired, such may be performed substantially immediately after sensorpositioning. For example, in certain embodiments a calibration protocolmay include a first post-positioning calibration at less than about 10hours after a sensor has been operably positioned, e.g., at less thanabout 5 hours, e.g., at less than about 3 hours, e.g., at less thanabout 1 hour, e.g., at less than about 0.5 hours. One or more additionalcalibrations may not be required, or may be performed at suitable timesthereafter.

The on-skin sensor control unit 44 may include an optional data storageunit 102 which may be used to hold data (e.g., measurements from thesensor or processed data).

In some embodiments of the invention, the analyte monitoring device 40includes only an on-skin control unit 44 and a sensor 42.

Referring back to FIG. 1, one or more receiver/display units 46, 48 maybe provided with the analyte monitoring device 40 for easy access to thedata generated by the sensor 42 and may, in some embodiments, processthe signals from the on-skin sensor control unit 44 to determine theconcentration or level of analyte in the subcutaneous tissue. As shownin FIG. 14, the receiver/display units 46, 48, typically include areceiver 150 to receive data from the on-skin sensor control unit 44, ananalyzer 152 to evaluate the data, a display 154 to provide informationto the patient, and an alarm system 156 to warn the patient when acondition arises. The receiver/display units 46, 48 may also optionallyinclude a data storage device 158, a transmitter 160, and/or an inputdevice 162.

Data received by the receiver 150 is then sent to an analyzer 152. Theoutput from the analyzer 152 is typically provided to a display 154. Thereceiver/display units 46, 48 may also include a number of optionalitems such as a data storage unit 158 to store data, a transmitter 160which can be used to transmit data, an input device 162, such as akeypad or keyboard. The receiver/display units 46, 48 may be a compacthandheld unit and also include a transceiver. In certain embodiments,the receiver/display unit 46, 48 is integrated with a calibration unit(not shown) and may include a conventional blood glucose meter.

In certain embodiments, analyte data (processed or not) may be forwarded(such as by communication) to a remote location such as a doctor'soffice if desired, and received there for further use (such as furtherprocessing).

Integration with a Drug Administration System

The subject invention also includes sensors including an antiglycolyticagent and a chelating agent, which sensors are used in sensor-based drugdelivery systems. The system may provide a drug to counteract the highor low level of the analyte in response to the signals from one or moresensors. Alternatively, the system may monitor the drug concentration toensure that the drug remains within a desired therapeutic range. Thedrug delivery system may include one or more (e.g., two or more)sensors, an on-skin sensor control unit, a receiver/display unit, a datastorage and controller module, and a drug administration system. In somecases, the receiver/display unit, data storage and controller module,and drug administration system may be integrated in a single unit. Thesensor-based drug delivery system uses data form the one or more sensorsto provide necessary input for a control algorithm/mechanism in the datastorage and controller module to adjust the administration of drugs. Asan example, a glucose sensor could be used to control and adjust theadministration of insulin.

Finally, kits for use in practicing the subject invention are alsoprovided. The subject kits may include an antiglycolytic agent orprecursor thereof in any suitable form as described herein. For example,a kit may include one or more antiglycolytic sensors as describedherein, and/or other structure that includes an antiglycolytic agent orprecursor thereof. In certain embodiments, a kit may include anantiglycolytic agent or precursor thereof adapted for transdermal orparenteral administration. Embodiments may also include a sensorinsertion device and/or transmitter and/or receiver.

In addition to one or more sensors, the subject kits may also includewritten instructions for using a sensor. The instructions may be printedon a substrate, such as paper or plastic, etc. As such, the instructionsmay be present in the kits as a package insert, in the labeling of thecontainer of the kit or components thereof (i.e., associated with thepackaging or sub-packaging) etc. In other embodiments, the instructionsare present as an electronic storage data file present on a suitablecomputer readable storage medium, e.g., CD-ROM, diskette, etc. In yetother embodiments, the actual instructions are not present in the kit,but means for obtaining the instructions from a remote source, e.g. viathe Internet, are provided. An example of this embodiment is a kit thatincludes a web address where the instructions can be viewed and/or fromwhich the instructions can be downloaded. As with the instructions, thismeans for obtaining the instructions is recorded on a suitablesubstrate.

In many embodiments of the subject kits, the components of the kit arepackaged in a kit containment element to make a single, easily handledunit, where the kit containment element, e.g., box or analogousstructure, may or may not be an airtight container, e.g., to furtherpreserve the one or more sensors and additional reagents (e.g., controlsolutions), if present, until use.

The following examples are offered by way of illustration and not by wayof limitation.

EXPERIMENTAL

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the embodiments of the invention, and are not intended tolimit the scope of what the inventors regard as their invention. Effortshave been made to ensure accuracy with respect to numbers used (e.g.amounts, temperature, etc.) but some experimental errors and deviationsshould be accounted for. Unless indicated otherwise, parts are parts byweight, molecular weight is weight average molecular weight, temperatureis in degrees Centigrade, and pressure is at or near atmospheric.

The following experiments demonstrate that blood glucose concentrationscan be substantially lowered in the vicinity of blood clots and furtherthat sensors that include antiglycolytic agents can delay and/or reducethe lowering so that such sensors do not exhibit the period of lowreading observed with sensors that do not include an antiglycolyticagent. In this manner, it is demonstrated that clinically accurateanalyte readings may be obtained from such sensors substantiallyimmediately after inserting the sensor.

FIGS. 15A, 15B, 15C and 15D show the experimental set-up for measuringglucose levels using platelet-rich plasma, heparinized whole blood, andnon heparinized whole blood, respectively.

Glucose sensors are inserted into small silicon tubes containing theappropriate biological fluid. The tubes are maintained at about 37degrees Celsius, and the glucose sensor is monitored. FIG. 15D shows theformation of a blood clot around the sensor.

As shown in FIG. 15E, the platelet-rich plasma shows a nearly constantglucose response, consistent with the lack of glucose-consuming redcells. The heparinized (non clotted) blood shows depletion over about a15 hour period, consistent with rates of glycolysis inanticoagulant-containing blood. The clotted blood shows a much morerapid depletion (within about 1.5-2 hours), consistent with localizeddepletion by the highly concentrated red cells in the clot surroundingthe sensor.

In the case of the clot, simple obstruction of the sensor surface by animpermeable clot is ruled out as a source of glucose depletion becausethe depletion rate (as a percentage of total current) varies withglucose concentration. High glucose samples take longer to deplete thanlower glucose samples. This is consistent with active consumption ofglucose by the surrounding clot.

FIG. 16 shows that even modest amounts of an antiglycolytic agent,included into a glucose sensor, can greatly retard, if not minimize,glucose consumption by a blood clot which surrounds the sensor.Antiglycolytic sensors were prepared by modification of control sensors(FREESTYLE NAVIGATOR®) as follows. A coating solution was prepared from250 mg/mL of a racemic mixture of L-glyceraldehyde and D-glyceraldehyde,and 150 mg/mL in polymer PC-1306 (Biocompatibles, PLC), the formersuspended and the latter dissolved in ethanol. The resultingantiglycolytic sensors had approximately 138 micrograms of the racemicmixture of D- and L-glyceraldehydes incorporated as a thin, outercoating. Both these sensors and control sensors (no antiglycolyticagents added) were then inserted into blood clots, and the currentresponse was followed over time.

As the graph of FIG. 16 shows, the control sensors show thepreviously-observed about 2 hour glucose depletion period. The depletionis much delayed (up to about 12 hours) in the glyceraldehydes-containingsensors. This demonstrates that the glyceraldehydes are beingincorporated into the red cells adjacent to the sensor, and are reducingglucose consumption by the adjacent red blood cells.

A further example of the use of an antiglycolytic sensor is provided byits use in an in vivo environment. In this example, a control sensor(FREESTYLE NAVIGATOR®) is inserted in the arm of a non-diabetic subject,adjacent to a similar sensor, which has been modified by the addition ofan antiglycolytic agent, L-glyceraldehyde. A coating solution was made200 mg/mL in L-glyceraldehyde, and 150 mg/mL in polymer PC-1306(Biocompatibles, PLC), both dissolved in ethanol. The FREESTYLENAVIGATOR® sensor was then modified by dipping twice into this coatingsolution, yielding an overcoat containing about 55 micrograms ofL-glyceraldehyde.

FIG. 17 shows the performance of these two sensors, implanted side byside in the arm of a non-diabetic subject. Note that the control sensorshows a large negative deviation (to values well below 60 mg/dL) insignal during the night, while the antiglycolytic-modified sensor doesnot. Glucose readings below 60 mg/dL are not anticipated in non-diabeticsubjects, and are therefore considered to be anomalous, reflectingeither (a) sensor malfunctions, or more likely (b) local inhomogeneitiesof glucose concentration (in the vicinity of a wound, for example)wherein the glucose concentration deviates substantially from thesystemic value. Such deviations are observed with some regularity incontrol sensors, but are not observed in sensors modified withL-glyceraldehyde.

An example of the use of an antiglycolytic sensor containing borateminerals, boric acid or any precursor thereof, is provided by itstesting in an in vitro environment. 50 mg/ml boric acid was mixed with150 mg/ml L-glyceraldehyde and 150 mg/mL PC in 100% ethanol. The sensorwas dipped three times with a 10 minute interval. The sensor was thencured overnight, and subjected to stress at 56° C. for nine days andsubsequently tested in nonheparin blood. FIG. 18 shows that the highbackground current is reduced significantly by adding borate to theformulation.

It is evident from the above results and discussion that theabove-described invention provides devices and methods for continuousanalyte monitoring. The above-described invention provides a number ofadvantages some of which are described above and which include, but arenot limited to, the ability to provide clinically accurate analyte datawithout a substantial time delay after operably positioning the sensorin a patient or frequent calibrations. As such, the subject inventionrepresents a significant contribution to the art.

While embodiments of the invention have been described with reference tothe specific embodiments thereof, it should be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation, material, composition of matter, process, processstep or steps, to the objective, spirit and scope of the presentinvention. All such modifications are intended to be within the scope ofthe claims appended hereto.

1. A glucose sensor comprising: a working electrode comprising a sensinglayer disposed thereon, the sensing layer comprising a glucoseresponsive enzyme; a counter electrode; and an active agent and achelating agent positioned proximate to the working electrode, theactive agent comprising an antiglycolytic agent or precursor thereof. 2.The glucose sensor of claim 1, wherein the active agent is chemicallybonded to the chelating agent.
 3. The glucose sensor of claim 1, whereinthe active agent is selected from the group consisting of a fluoride, aglyceraldehyde, mannose, glucosamine, mannoheptulose,sorbose-6-phophate, trehalose-6-phosphate, maleimide, an iodoacetate,and any combination thereof.
 4. The glucose sensor of claim 1, whereinthe active agent is a glyceraldehyde.
 5. The glucose sensor of claim 4,wherein the glyceraldehyde is present in the range of from about 1microgram to about 2 milligrams.
 6. The glucose sensor of claim 1,wherein the chelating agent is selected from the group consisting ofborate, boric acid, a main group metal, a transition group metal, agroup IIIA metal, and any combination thereof.
 7. The glucose sensor ofclaim 1, wherein the chelating agent is boric acid.
 8. The glucosesensor of claim 7, wherein the boric acid is present in the range offrom about 0.1 microgram to about 1 milligram.
 9. The glucose sensor ofclaim 1, wherein the sensing layer comprises an electron transfer agent.10. A glucose sensor comprising: a working electrode comprising asensing layer disposed thereon, the sensing layer comprising a glucoseresponsive enzyme; a counter electrode; and a membrane disposed over atleast a portion of the sensing layer, the membrane comprising an activeagent and a chelating agent, and the active agent comprising anantiglycolytic agent or precursor thereof.
 11. The glucose sensor ofclaim 1, wherein the active agent is chemically bonded to the chelatingagent.
 12. The glucose sensor of claim 1, wherein the active agent isselected from the group consisting of a fluoride, a glyceraldehyde,mannose, glucosamine, mannoheptulose, sorbose-6-phophate,trehalose-6-phosphate, maleimide, an iodoacetate, and any combinationthereof.
 13. The glucose sensor of claim 1, wherein the active agent isa glyceraldehyde.
 14. The glucose sensor of claim 4, wherein theglyceraldehyde is present in the range of from about 1 microgram toabout 2 milligrams.
 15. The glucose sensor of claim 1, wherein thechelating agent is selected from the group consisting of borate, boricacid, a main group metal, a transition group metal, a group IIIA metal,and any combination thereof.
 16. The glucose sensor of claim 1, whereinthe chelating agent is boric acid.
 17. The glucose sensor of claim 7,wherein the boric acid is present in the range of from about 0.1microgram to about 1 milligram.
 18. The glucose sensor of claim 1,wherein the sensing layer comprises an electron transfer agent.
 19. Theglucose sensor of claim 1, wherein at least the active agent is timereleased from the membrane.
 20. The glucose sensor of claim 1, whereinthe membrane is a mass transfer limiting membrane.